Add support for blocking contacts and accounts (#260)

* Add blockContact and unblockContact subcommands

* Send blocked status in contacts sync

* Use only one method for blocking and unblocking

* Add blocking/unblocking for groups

* Prevent blocked messages from being printed

* Print blocked property in listContacts and listGroups commands

* Handle BlockedListMessages

* Store blocked state from incoming contact and group sync messages

* Minor changes and corrections

* Add block and unblock commands to man file (and also fix some headings of commands)

src/main/java/org/asamk/signal/commands/UnblockCommand.java

@@ -0,0 +1,52 @@
+package org.asamk.signal.commands;
+
+import net.sourceforge.argparse4j.inf.Namespace;
+import net.sourceforge.argparse4j.inf.Subparser;
+import org.asamk.signal.GroupIdFormatException;
+import org.asamk.signal.GroupNotFoundException;
+import org.asamk.signal.manager.Manager;
+import org.asamk.signal.util.Util;
+import org.whispersystems.signalservice.api.util.InvalidNumberException;
+
+public class UnblockCommand implements LocalCommand {
+
+    @Override
+    public void attachToSubparser(final Subparser subparser) {
+        subparser.addArgument("contact")
+                .help("Contact number")
+                .nargs("*");
+        subparser.addArgument("-g", "--group")
+                .help("Group ID")
+                .nargs("*");
+        subparser.help("Unblock the given contacts or groups (messages will be received again)");
+    }
+
+    @Override
+    public int handleCommand(final Namespace ns, final Manager m) {
+        if (!m.isRegistered()) {
+            System.err.println("User is not registered.");
+            return 1;
+        }
+
+        for (String contact_number : ns.<String>getList("contact")) {
+            try {
+                m.setContactBlocked(contact_number, false);
+            } catch (InvalidNumberException e) {
+                System.err.println(e.getMessage());
+            }
+        }
+
+        if (ns.<String>getList("group") != null) {
+            for (String groupIdString : ns.<String>getList("group")) {
+                try {
+                    byte[] groupId = Util.decodeGroupId(groupIdString);
+                    m.setGroupBlocked(groupId, false);
+                } catch (GroupIdFormatException | GroupNotFoundException e) {
+                    System.err.println(e.getMessage());
+                }
+            }
+        }
+
+        return 0;
+    }
+}